This hand drawn graph with its own cool story plotted in the style of a waterfall plot, in the Cambridge Encyclopedia of Astronomyhttp://www.joydiv.org/up.htm

But a plot of what?

In July 1967, astronomers at the Cavendish Laboratory in Cambridge, observed an unidentified radio signal from interstellar space, which flashed periodically every 1.33730 seconds. This object flashed with such regularity that it was accurate enough to be used as a clock and only be off by one part in a hundred million.

It was eventually determined that this was the first discovery of a pulsar CP-1919. This is an object that has about the same mass as the Sun, but is the size of the San Francisco Bay at its widest (~20 kilometers) that is rotating so fast that its emitting a beam of light towards Earth like a strobing light house! Pulsars are neutron stars that are formed from the remnants of a massive star when it experiences stellar death.